Sema: Properly support Microsoft-mode template arguments

Summary:
There were two things known to be wrong with our implementation of MSVC
mode template arguments:

- We didn't properly handle __uuidof/CXXUuidofExpr and skipped all type
  checking completely.
- We didn't allow for MSVC's extension of allowing certain constant
  "foldable" expressions from showing up in template arguments.
  They allow various casts dereference and address-of operations.
  We can make it more general as we find further peculiarities but this
  is the known extent.

Reviewers: rsmith, doug.gregor, rjmccall

Reviewed By: doug.gregor

CC: cfe-commits, rnk

Differential Revision: http://llvm-reviews.chandlerc.com/D1444